Bone cements and calcium phosphate cements are the two major groups of cementing materials that are currently being used for the fixation of broken bones or artificial joints in human.
Bone cements are normally made from polymethylmetacrylate (PMMA)—a polymer material, with ceramics filler, for example zirconium oxide or barium sulphate. It is used for fixation of artificial joints to the skeleton. Basically, the bone cements are two-component materials, i.e. consists of pre-polymerized PMMA plus fillers in the form of a powder, and another is a monomer liquid. There are many drawbacks to these bone cements, such as polymerization which develops temporary heat between 60° C. to 100° C. that is found detrimental to the surrounding tissues, as cells cannot survive temperatures over 47° C. Bone cements are brittle and prone to fatigue failure. They are mechanically weak when they entrap impurities such as air and blood. They produce “wear debris” that can cause osteolysis (i.e., bone resorption). Bone cements may support colonisation of bacteria and development of post-operative infections. They may also cause allergy and anaphylactic reaction during surgery.
Calcium phosphate (CaP) cements consists of calcium phosphate precursors mixed with a setting solution to form calcium phosphate paste or dough that eventually hardened into solid material. There are various combinations of calcium phosphate precursors, such as CaHPO4.2H2O, CaHPO4, Ca2P2O7, Ca2H2P2O8, etc. Some of the powder mixtures may need to be heated to temperatures up to 1000° C. before mixing with the setting solution. The setting solutions could be in turns of basic aqueous solutions, acidic aqueous solutions, solvents or water. Other than these calcium phosphate precursors, fillers (e.g. MgO, strontium, collagen), accelerator agents (e.g. LiCl, LiOH), retarder agents (e.g. polysaccharide, glycerine, starch) and pH controlling agents (e.g. HCl, HNO3, NH3O4, Na2HPO4, etc.,) were also used.
There are few drawbacks to CaP cements, such as hardening reaction temperatures ranging between 30-150° C. For temperatures exceeding 45° C., these are detrimental to the surrounding tissues since cells cannot survive temperatures over 47° C. The pH of the CaP cements ranges between acidic to highly basic (pH ˜5-12). In micro-environment, these could be detrimental causing irritation and inflammatory reactions to the surrounding cells which requires pH ˜7 for the body homeostasis. Thus, it may take a very long time to reach neutral pH. Usage of complex chemicals may also affect the biocompatibility properties of the CaP cements, apart from it being more difficult or more expensive to produce. Some of the cements take very long time to degrade. Controlled degradation is favorable so that the body can have time to replace the synthetic materials with the host bone. Too fast or too slow resorption is both unfavourable. Therefore there is a need for an invention that can achieve one or more of the following objectives which constitutes the objectives of the present invention i.e.                1. To produce a self-hardened apatite (SHA) cement which is biodegradable, biocompatible and bioactive in the body, as well as to enhance bone growth and bone integration;        2. To produce a self-hardened apatite (SHA) cement which has neutral pH (˜7);        3. To produce a self-hardened apatite (SHA) cement which has compressive strength of between 10-30 MPa, which is suitable for both non-load bearing and some load bearing applications;        4. The hardening or setting process of the cement composition should not generate heat greater than 37° C., which is the normal body temperature; and        5. The self-hardened apatite cement is also suitable to be used as a delivery vehicle.        